The present invention related to silver salt photothermographic dry imaging materials exhibiting enhanced image quality and superior storage stability and in particular to black-and-white silver salt photothermographic dry imaging materials (hereinafter, also denoted as photothermographic imaging materials or simply as photothermographic materials), exhibiting enhanced image quality and superior silver image lasting property.
In the field of graphic arts and medical treatment, there have been concerns in processing of photographic film with respect to effluents produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. There has been desired a photothermographic material for photographic use, capable of forming distinct black images exhibiting high sharpness, enabling efficient exposure by means of a laser imager or a laser image setter.
Known as such a technique is a thermally developable photothermographic material which comprises on a support an organic silver salt, light sensitive silver halide grains, and reducing agent, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075, and D. Morgan, xe2x80x9cDry Silver Photographic Materialsxe2x80x9d (Handbook of Imaging Materials, Marcel Dekker, Inc. page 48, 1991). In such photothermographic materials, no solution type processing chemicals is used, providing a simple and environment friendly system to users.
Usually, a photothermographic imaging material comprises a support provided thereon at least two functional layers comprised of an image forming layer and at least a protective layer. Silver salt photothermographic materials which are capable of forming a high density image at a relative low silver content are attractive to manufactures, for the amount of silver necessary for maintaining a given optical density is reduced, reducing the amount of emulsion used in coating, thereby reducing loads on coating and drying and enhancing productivity. Further, reduction of the silver amount enables cost savings of the photothermographic material. However, it is rather difficult to achieve reduction of the silver amount, while at the same time maintaining high photographic performance, so that a technique effective for improving it has been desired.
With regard to outputted images used for medical diagnosis, it has been supposed that more exact diagnostic observation results can be easily achieved with cold image tone. The cold image tone refers to pure black tone or bluish black tone and the warm image tone refers to a brownish black image exhibiting a warm tone.
Such a photothermographic material contains a reducible light-insensitive silver source (such as organic silver salts), a catalytically active amount of photocatalyst (such as silver halide) and a reducing agent, which are dispersed in a binder matrix. Such photothermographic materials are stable at ordinary temperature and, after exposure, form silver upon heating at a relatively high temperature (e.g., 80xc2x0 C. or higher) through an oxidation reduction reaction between the reducible silver source (which functions as an oxidizing agent) and the reducing agent. The oxidation reduction reaction is accelerated by catalytic action of a latent image produced by the exposure. Silver formed through reaction of the reducible silver salt in exposed areas provides a black image, which contrasts with non-exposes areas, leading to image formation.
Antifoggants to minimizing fogging of images are optionally incorporated into the photothermographic material. As one of the most effective techniques for antifogging is cited incorporation of polyhalogenide compounds described in JP-A Nos. 9-160164, 9-244178, 9-258367, 9-265150, 9-281640 and 9-319022 (hereinafter, the term, JP-A means an unexamined, published Japanese Patent Application). However, problems arose with the application of such compounds to photothermographic imaging materials used in a laser imager for medical use, such that deteriorations in image aging stability, such as increased fogging after storage were noticed or a silver image tone changed to a yellowish warm tone. Known as a technique for improving image color tone is incorporation of a dye into a photothermographic material or a support. Image toning agents (or tone modifying agents) are also commonly known, as described in U.S. Pat. Nos. 4,132,282, 3,994,732, 3,846,136 and 4,021,249. However, such improvement means are insufficient for image tone for medical use and a further improvement is desired to enhance diagnosis levels, but effective improving technique is not achieved as yet.
In view of the foregoing, it is an object of the present invention to provide a photothermographic imaging material exhibiting enhanced image quality and superior image tone and image lasting property, while having a relatively low silver content, and an image recording method by the use of the same.
The object of the invention can be accomplished by the following constitution:
a silver salt photothermographic dry imaging material comprising a light sensitive layer and a light insensitive layer, the light sensitive layer comprising organic silver salt grains, a light sensitive emulsion containing light sensitive silver halide grains and a solvent, a reducing agent and a binder, characterized in that at least one of the light sensitive layer and the light insensitive layer contains a silver saving agent and an image obtained by thermal development at 123xc2x0 C. for 13.5 sec. exhibits an average contrast of 2.0 to 6.0 within the diffuse density range of 0.25 to 2.0 on a characteristic curve represented on orthogonal coordinates in which a unit length of a diffuse density (Y-coordinate) and that of common logarithmic exposure (X-coordinate) are equivalent to each other.
Further, preferred embodiments of the silver salt photothermographic dry imaging material include (2) the material having a total silver amount of 0.7 to 1.2 per m2 of the material, (3) comprising at least two light sensitive layers, (4) containing at least two compounds capable of generating a labile species capable of oxidizing silver or deactivating the reducing agent which is incapable of reducing silver ions of the organic silver salt, upon exposure to ultraviolet light or visible light, (5) the light sensitive layer being formed by using a coating solution to form the light sensitive layer, containing at least 30% by weight of water, (6) meeting the requirement of 190xc2x0 less than hab less than 260xc2x0, in which hab is a hue angle (as defined in JIS-Z 8729) and (7) exhibiting a correlated color temperature of 5000 to 6000xc2x0 K with respect to light transmitted through the photothermographic material film placed on a viewing box using a white fluorescent lamp.
Furthermore, when recording an image on the photothermographic dry imaging material, exposure is conducted preferably using a laser light scanning exposure machine (8) employing double beam scanning laser light or (9) longitudinal multiple laser scanning light.